That may be really involved.
It may be just easier to buy a wireless game adapter like the Linksys WGA54G. You plug in your NIC into it and the units's antenna then connects you to your wireless network.
- You'll have to assign a network address to the Linux box, or get the Vista laptop to be a DHCP server.
- Then you have to set up routing on the vista Laptop.
- Your home router may not NAT the IP address you assigned to the Linux box and then you won't get access to the net. Either you modify the configuration of the router or you get the Vista box to NAT the IP address of the Linux box to an address in the range of the router's LAN interface.
You could also consider adding a wireless card to your Linux box. Ubuntu's support for ndiswrapper is fairly good.